The present invention relates generally to the field of agriculture and horticulture and, more particularly, to a barrier, enclosure and method designed to protect plants and crops from infestation by insects, particularly Thysanoptera thripidae, also known as thrips.
Thrips are distributed worldwide and are important crop pests and vectors of viral diseases. Damage to commercial crops from thrips is estimated worldwide in the tens of millions of dollars per year.
The word Thysanoptera comes from the Greek xe2x80x98thysanosxe2x80x99, meaning a fringe, and xe2x80x98pteronxe2x80x99, meaning a wing. Accordingly, thrips are highly mobile fringe-winged insects. There are presently at least 6,000 active species of thrips in the world.
Thrips are very small, elongate, cylindrical, gregarious insects ranging from {fraction (1/25)} to xe2x85x9 inch in length. Males are usually smaller than females. The nymphs are frequently pale yellow and highly active. The antennae and legs are relatively short. Adults are usually black or yellow-brown, but may have red, black or white markings and often jump when disturbed. They may have wings or may be wingless. If wings are present, they are long, narrow and fringed with hairs. Winged varieties often ride air currents in order to disperse widely, having a predisposition towards thunder storms as a suitable time of flight. Hence, they are referred to as xe2x80x98Thunder fliesxe2x80x99 or xe2x80x98Thunder Bugsxe2x80x99 in some locations.
Thrips have asymmetrical mouthparts, having only one (the left) mandible, short 6 to 10 segmented antennae and no cerci. Their wings when present are nearly equal, very thin with little venation and a lot of hairs making a fringe around the edge which greatly increase the effective size of the wings. Fully winged, brachypterous (with reduced wings) and apterous (wingless) forms may occur in the same species.
Thrips mouthparts are designed for piercing and sucking. Most species feed on plant sap. To obtain sap, a thrips will make an incision in a single cell with the left mandible and then insert the maxillae and hypo pharynx and pump out the juices of this and adjacent cells using a pharyngeal pump.
Thrips breeding inflicts further damage on plants. Females of some suborders are equipped with ovipositors which are used to cut slits into plant tissue into which eggs are inserted. Females of other suborders lack ovipositors and lay their eggs on the outside of plants, either singly or in small groups.
Thrips undergo gradual metamorphosis. A typical thrips life cycle is as follows. Each female lays 25 to 50 eggs which hatch in two to seven days into active nymphs. Parthenogenesis (where ova develop and mature into female nymphs without fertilization) occurs in many species. Nymphs resemble adults, but lack wings and are lightly colored. The nymphal stage is followed by two resting stages: the prepupa and pupa. The resting stages can be found either on the host plant or in the soil below the host plant. Under favorable conditions, the developmental period from egg to adult ranges from eleven days to three weeks depending on the species. Hence, a population may increase quite rapidly.
The Onion Thrips and the Western Flower Thrips are the most crop-damaging species in the U.S.A., Europe and the Middle East, both for the damage caused by their eating and reproductive behavior and because they are known vectors of plant diseases, the most important of which for greenhouse crops are impatiens necrotic spot virus and tomato spotted wilt virus. When thrips feed on plants infected with these diseases, they transmit the diseases to other plants in the greenhouse. Once plants are infected, it is too late to do anything except dispose of diseased plants.
Tolerance of thrips on floriculture crops is particularly low, as thrips infestation results in deformation of flowers and leaves. Flower buds often abort in heavy infestations. Thrips feed on both foliage and flowers, as well as young tissues in shoot apexes where the leaves are expanding. By puncturing the plant and withdrawing cell sap, they cause bleached, silvered or deformed leaves and necrotic spots or blotches on flower petals. Eventually the damaged foliage becomes papery, wilts and drops prematurely. In addition, thrips produce large quantities of a varnish-like excrement which collects on leaves, creating an unsightly appearance.
Thrips are one of the most difficult pests to control in greenhouses. They are tiny insects that reproduce rapidly, eat voraciously and can easily and swiftly devastate an entire crop. Accordingly, many different practices are presently in use to prevent or control thrips infestation. Control measures to date include biological measures such as the introduction of predacious insects. For example, adult female predatory mites (Neoseiulus) consume from 1 to 10 young thrips per day and have a 30-day lifespan. Adult pirate bugs (Orius) consume 5-20 thrips (all stages) per day. Orius is the only predator that attacks thrips in tight places like flower buds. Soil-dwelling predacious mites (Hypoaspsis) attack thrips in their pre-pupal and pupal stages when they inhabit the soil or growing medium. Thripobius semiluteus is a parasitoid of thrips nymphs.
Also in limited use are cultural controls, such as providing a fallow period in summer by removing all plants and heating the greenhouse until soil temperatures reach 60xc2x0 F. for three weeks. During this time, thrips eggs will hatch and the nymphs will starve for lack of food. Another cultural control is to remove all flowers and buds, if not crucial to the crop. A further cultural measure is to introduce plants, such as garlic, that repel thrips.
There are many different pesticides in use, including xe2x80x9cbiorationalxe2x80x9d pesticides, which are used by growers relying on organic pest management. However, thrips control is difficult with the use of pesticides, as during much of their life cycle thrips exist as eggs, as pupae in the soil, or as extremely mobile adults. Once thrips infest a crop, the adult females begin feeding and laying their eggs. Thrips usually concentrate on rapidly growing tissues such as young leaves, flowers and terminal buds. This affinity for tight places makes thorough coverage with a pesticide difficult.
Agricultural researchers have experimented with other measures to repel thrips by interfering with their visual cues with limited success. Reflectance of visible light was found to repel xanthophyllous thrips from the surface of certain colors, as described in an article by Matteson, N., Terry, L (1992). Response to color by male and female Frankliniella occidentalis during swarming and non-swarming behavior. Entomol. Exper. App. 63:187-201. Apparently, thrips are more attracted to some colors than to others. This research does not, however, demonstrate a repellant property of any particular color other than relative to other colors.
The use of UV absorbing materials has been found to be of assistance in repelling crop-damaging insects and is in use in commercial growing of field crops. UV absorbing screens and films are used as roof coverings in conjunction with wall coverings of conventional insect-excluding netting. This phenomenon is discussed extensively in a recent professional publication: Antigenus, Y., Lapidot, M., Hadar, D., Messika, Y, Coen, S. (1998). Ultraviolet-absorbing screens serve as optical barriers to protect crops from virus and insect pests. J. Econ. Entomol. 91: 1401-1405. The studies were not conclusive, however, in demonstrating a repellant effect as opposed to a camouflaging property and it is conceded in this publication that such films and combinations of films and nets do not provide totally effective exclusion unless the nets have a mesh size that is sufficiently small to constitute a physical barrier.
Further attempts at visual manipulation include the use of reflective colored mulches around the base of plants. These measures were also shown to reduce thrips infestations and tomato spotted wilt virus incidence in crops, as described in the aforecited articles by Brown and Brown, 1992; Greenoug, 1985; Scott et al., 1989; and Staviski et al., 2000. It is known that thrips congregate on the underside of leaves and petals. Apparently, the reflective mulch provides a light source beneath the plants which disturbs them. However, such light reflective colors have not been used in screens.
Accordingly, in light of the limited success of the measures described above, insect-excluding screens have been the preferred method of fighting thrips infestation. This too, however, has achieved only limited success, and thrips remain a major agricultural pest. In 1995, researchers from North Carolina reported that 27 types of insect screens were evaluated for thrips exclusion. Only 3 brands (FLYBARR(copyright), BUGBED(copyright) and NO-THRIPS(copyright)) were somewhat effective in preventing the entry of thrips into greenhouses.
In order to exclude thrips, screens must have a fine mesh. Typical thrips screens have mesh in excess of of fifty openings per inch, consistent with the small size of the insect. Such screens have a number of inherent limitations due to their restriction of air flow, including higher static pressure drops, inadequate air exchange, higher energy consumption by ventilation fans, excessive wear on fan motors, and higher greenhouse temperatures. Therefore, agriculturalists have been forced to strike a balance between screens with very fine mesh that physically exclude thrips and more open screens that permit needed airflow, but also permit limited entry of thrips and other insects.
As a result, many different screens have been tried, none of which provide a totally satisfactory solution to thrips infestation. U.S. Pat. Nos. 5,007,196 and 6,341,444 disclose electrically charged screens for insect exclusion, the former disposed at the base of a structure to repel crawling insects and the latter as window screens to repel flying insects. Such screens are not practical for the extensive coverage needed by large greenhouses in use in commercial agricultural and horticultural applications. International Patent Application Publication No. WO 98/28966 shows a net made of a transparent or translucent polymeric material in which there is incorporated a substance which absorbs UV light. It was found that nets which incorporate such a substance provide a more effective exclusion than nets without such a substance, presumably because of an optical quality that interferes with the vision of the insects. This is not proven and remains a presumption. A further variation of an insect excluding net is ALUMINET(trademark), produced by Polysack Plastic Industries, Ltd. of Israel, which incorporates a thin aluminum strand periodically within the weave of the net, also presumably for an optical effect.
Additional information concerning thrips control can be found in the following publications, which are incorporated herein by reference:
Anonymous. (1988). Ad Hoc Panel on control of Frankliniella occidentalis. European and Mediterranean Plant Protection Organization, Mimeograph. 34 pp.
Berlinger, M. J, Dahan, R., (1989). In: (R. Cavalloro C. Pelerents (Eds.) Integrated Pest Management In Protected Vegetable Crops. Proc. CEC/IOBC group meeting/Cabrils, May 27-29, 1987.A. A Balkema/Rotterdam/Brookfield.
Belinger, M. J, Mordecchi, S., Leeper, A. (1991). Application of screens to prevent whitefly penetration into greenhouses in Mediterranean Basin. IOBC/WPRS Bull. XIV. 105-110.
Berlinger, M. J, Lebiush-Mordechi, S., Fridja, D., Mor, N. (1993). The effect of types of greenhouse screens on the presence of western flower thrips: a preliminary study. Proc. Working Group Integrated Control in Glasshouses Pacific Grove, Calif., U.S.A. Apr. 25-29, 1993 IOBC/WPRS Bull. Vol. 16: 13-16.
Bomer, B. (1989). Frankliniella, Early recognition and treatment Deutscher-Gartenbau 43 (4): 207-211.
Broadbent, A. B., Matteoni, J. A., Allen., W. R., (1990). Feeding preferences of the western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae) and incidence of Tomato Spotted Wilt Virus among cultivars of florits chrysanthemum. Can Ant. 122:1111-1117.
Brodgaard, H. F., (1989). Colored sticky traps for Frankliniella occidentalis (Pergande) (thysanoptera: Thripidae) in glasshouses. J. Appl. Entomol. 107: 136-140.
Brown, S. L., Brown, J. E., (1992). Effect of plastic mulch color and insecticides on thrips populations and damage to tomatoes. Hort Technology 2(2):208-211.
Bryan., D. E., Smith, R. F. (1956) The Frankliniella occidentalis complex in California (Thysanoptera: Thripidae). University of California Publication in Entomology 10: 359-410.
Chyzik, R., Klein, M., Ben-Dov, Y., Cohen, A. (1993) Proc. 1993 Int. Conf. Thysanoptera, S. Burlington, Vt., USA.
Greenoug, D. R., (1985). Aluminum-surfaced mulch and disease resistance: Approaches to the control of tomato spotted wilt virus in solanaceous crops. MS. Thesis, Louisiana State Univ., Baton Rouge.
Hadar, D, (1997). The net is cover all over the crops. Hasade 77:68-69.
Hadar, D., Nestel, D. (1997). Utilization of Insect-Proof Nets in Israeli Agriculture. Phytoparasitica 25(2): 148-149.
Horowits, R., Forer, G., Ishaaya, I. (1994). Managing resistance in B. tabaci In Israel with emphasis on cotton. Pesticides Sci. 42: 113-112.
Leuprecht, B. (1988). A new pest under glass. Flower thrips on vegetable crops. Gemuse-Munchen. 24 (6): 274-277.
Matteson, N., Terry, I. (1992). Response to color by male and female Frankliniella occidentalis during swarming and non-swarming behavior. Entomol. Exper. App. 63:187-201.
Matteson, N., Terry, I., Ascoli, C. A., Gilbert, C. (1992). Spectral efficiency of the western flower thrips, Frankliniella occidentalis. J. Ins. Physiol. 38(453-459.
Mazza, C. A., Zavala, J., Scopel, A. L., Ballare, C. L. (1999). Perception of solar UVB radiation by phytophagous insects: Behavioral responses and ecosystem implications Proc. Natl. Acad. Sci. USA 96(3):980-985.
Mentel, W. P., (1989). Bibliography of the western flower thrips, Frankliniella occidentalis (Pergande) (Thysanoptera: Thripidae). Section Reg. Ouest palearctique/West Palaearctic Reg. Section Bul. 1989/XII/3: 29-66.
Moffitt, H. R., (1964). A color preferences of the western flower thrips, Frankliniella occidentalis. J. Econ. Entomol. 57: 604-605.
Scott, S. J, McLeod, P. J, Montgomery, F. W., Handler, C. A.(1989). Influence of reflective mulch on incidence of thrips (thysanoptera: Thripidae: Phlaeothripidae) in staked tomatoes. J. Entomol. Sci. 24(4): 422-427.
Stavisky, J, Funderburk, J, Olson, S., Momol, T. (2000). UV-Reflective Mulch as an IPM Tactic for Thrips and Tomato Spotted Wilt Virus in Tomato and Pepper in Florida. Nor. Flor. Res. Ed. Cent. 2(21): 3-4.
VanLenteren, J. C., Wardlow, L. R., (eds). 1989) Proc. IOBC/WPGR workshop on biological control of pests in ornamentals in greenhouses, Alsmeer, the Netherlands, Dec. 14-17, 1987. Section Reg. Ouest Paleartique/West Palaeartic Reg. Section Bul. 1989/XLL/3.
Vernon, R. S., Gillespie, D. R. (1990). Spectral responsiveness of Frankliniella occidentalis (Thysanoptera:Thripidae) determined by trap catches in greenhouses. Envir. Entomol. 19(5):1229-1241.
Walker, W. F., (1974). Responses of selected Thlysanoptera to colored surfaced. Envir. Entomol. 3: 295-304.
Watterson, J. C., (1985). Tomato diseases, a practical guide for seedsmen, growers, and agricultural advisors. Petoseed Co., Saticoy, Calif. P. 38.
Yudin, L. S., Mitchell, W. C., Cho, J J (1987). Color preferences of thrips (Thysanoptera: Thripidae) with reference to aphids (Homoptera: Aphididae) and leaf miners in Hawaiian lettuce farms. J. Econ. Entomol. 80:51-55.
Therefore, there is a widely recognized need for, and it would be highly advantageous to have, a screen that serves as an effective barrier to protect plants and crops from infestation by insects, particularly small insects such as thrips.
Accordingly, it is an object of the present invention to provide a simple screen that reflects light in certain wavelengths in order to repel insects, particularly thrips.
It is a further object of the present invention to provide an enclosure that protects plants and crops from infestation by insects, particularly thrips.
It is a yet further object of the present invention to provide a method for protecting plants and crops from infestation by insects, particularly thrips.
According to one aspect of the present invention there is provided a barrier for restricting insect passage therethrough, thrips in particular, the barrier comprising a screen having a plurality of openings therein, the screen being reflective of at least a portion of wavelengths of light impinging thereon, so as to repel the insects from the screen, thereby restricting insect passage through the barrier.
According to another aspect of the present invention there is provided an enclosure for enclosing at least one agricultural crop, the enclosure being at least partially formed of a barrier for restricting insect passage therethrough, thrips in particular, the barrier comprising a screen having a plurality of openings therein, the screen being reflective of at least a portion of wavelengths of light impinging thereon, so as to repel insects from the screen, thereby restricting insect passage through the barrier.
According to another aspect of the present invention there is provided a method for protecting at least one agricultural crop from insects, thrips in particular, the method comprising enclosing the agricultural crop in an enclosure at least partially formed of a barrier for restricting passage of insects therethrough, the barrier comprising a screen having a plurality of openings therein, the screen being reflective of at least a portion of wavelengths of light impinging thereon, so as to repel insects from the screen, thereby restricting insect passage through the barrier.
According to features in the described preferred embodiments the portion of wavelengths is in the ultra-violet light spectrum.
According to features in the described preferred embodiments the portion of wavelengths is between 320 nm and 400 nm.
According to features in the described preferred embodiments the screen is at least partially formed of material that reflects the light.
According to features in the described preferred embodiments the screen comprises an additive that reflects the light.
According to features in the described preferred embodiments the screen is at least partially coated with a coating that reflects the light.
According to features in the described preferred embodiments the barrier forms at least a portion of an enclosure from which the insect is to be restricted.
According to features in the described preferred embodiments the screen has 15-60 openings per inch length.
According to features in the described preferred embodiments the screen has about 50 openings per inch length.
According to features in the described preferred embodiments the screen comprises at least one UV reflective additive selected from the group consisting of
low density polyethylene;
TiO2 white pigment;
2-Hydroxy-4-n-octoxybenzophenoneUVA;
Poly[[6-(1,1,3,3-tetramethylbutyl)amino]-s-triazine-2,4-diyl][[2,2,6,6tetramethyl-4-piperidyl)imino]hexmethylene[(2,2,6,6-tetramthyl-4-piperidyl)imino]]; and
polymeric HALS.
According to features in the described preferred embodiments the screen comprises threads of aluminum foil.
The present invention successfully addresses the shortcomings of the presently known configurations by providing a barrier, an enclosure and a method that effectively protect plants and crops from infestation by insects, particularly thrips.